Bags for packaging which have a zipper tape closure are very popular. These bags can easily and repeatedly be opened and closed. It is generally expected in the market that a bag with a zipper tape will be used more and more in the future.
The conventional type of zipper tape is generally based on a polyethylene system or a polypropylene system, and a male strip and a female strip forming a pair extending in a row and used to form a mating section. The strips are integrally formed on a tape, and the tape is cut in use along a center line thereof to provide a slender section with a male strip and that with a female section. When this zipper tape is agglutinated in use to a bag 1 for packaging as shown in FIG. 1, the cross section taken along the line A—A in the figure is as shown in FIG. 2(A), and a tape section 4 with a male strip 3a and a female strip 3b formed thereon is based on a polyethylene system when a resin used for an innermost layer 5 of a bag 1 for packaging is a polyethylene-based one, while the tape section 4 is based on a polypropylene system when the resin for the innermost layer 5 is a polypropylene-based one.
However, the conventional type of zipper tape has the defects as described below.    a) At first, when the zipper tape 2 is produced by means of miscellaneous shape extrusion molding, the male strip 3a and the female strip 3b are respectively formed on the tape section 4 in an integrated state therewith as shown in FIG. 2(A), and in this production method, it is impossible to mold a plurality of male strips and a plurality of female strips simultaneously in batch, and the two types of strips are formed only as a pair by means of extrusion molding, so that the productivity is low.    b) When the zipper tape 2 is agglutinated to the bag 1 for packaging, when the innermost layer 5 of the bag 1 and the tape section 4 of the zipper tape 2 are jointed to each other by loading a pressure and heating the jointed section from the outside as shown in FIG. 2(A), as there is the risk that the tape section 4 itself may be fused there is no way but to make the thickness of the tape section 4 larger.
Because of the requirement described above, when a pressure and heat are applied from the outside for making side seals 1a, 1b of the bag 1 for packaging as shown in FIG. 2(B), the mating section 3 and the tape section 4 form together a fused resin block 3′, 4′, and the section expands, so that the pressure and heat required for sealing must be strong, which causes other sealed sections to be heated excessively. On the contrary, when the pressure and heat used for sealing are weak, the resin block 3′, 4′ is not fully fused such that pin holes are easily generated therein.    d) In the zipper tape 2 comprising the mating section 3 made from a polyethylene-based resin and the tape section 4, as the innermost layer 5 of the bag 1 for packaging is thermally fused only the polyethylene-based bag, so that the zipper tape 2 can not be used for a bag made from a polypropylene-based resin. On the other hand, the zipper tape 2 made from a polypropylene-based resin can not be used for the bag 1 made from a polyethylene-based resin, and therefore the zipper tape 2 must be selected according to a material used for forming the innermost layer 5 of the bag 1.
Improved types of zipper tapes have been disclosed for the purpose to solve the problems as described above. As the most representative technology, there is the technology in which a heat-insulating film 6 having a melting point higher than that of the tape section 4 is laminated on the tape section 4 of the zipper tape 2 and further a film 7 for thermal fusion having a melting point lower than that of the heat-insulating film 6 is laminated on the heat-insulating film 6 (Japanese Patent No. 1908600). Namely, in the zipper tape 2, which is applied to the bag 1 for packaging shown in FIG. 1, the cross section A—A is as shown in is enlarged form in FIG. 3(A), while the cross section A′—A′ is as shown in its enlarged form in FIG. 3(B).
With this improved type of zipper tape 2, some of the problems in the conventional technology have been solved, but the following ones are still left unsolved.    e) When the zipper tape 2 is produced by means of the miscellaneous shape extrusion molding, the male strip 3a and the female strip 3b are formed integrally on the tape section 4 respectively, so that there is no way but to form the two types of strips in a pair and in a row, so that the productivity is not improved.    f) When the innermost layer 5 of the bag 1 and the thermally-fused film 7 of the zipper tape 2 are pressed to each other and heated for sealing, the risk that the tape sections 4 facing to each other are thermally fused to each other is evaded because of the presence of the heat-insulating film 6 as shown in FIG. 3(A), and this improvement advantageously makes it possible to reduce the total thickness of the tape section 4, heat-insulating film 6, and thermally fused film 7 down to about 100μ.    g) When the side seals 1a, 1b are made in the bag 1, the thickness of the fused resin block 3′, 4′, where the mating section 3 and the tape section 4 are integrated to each other, is reduced in proportion to the reduced thickness of the tape section 4 as shown in FIG. 3(B), but the reduction in thickness is still insufficient.    h) In a case of the zipper tape 2 made from a polyethylene-based resin, also the thermally fused film 7 and the innermost layer 5 of the bag 1 must be made from the polyethylene-based resin, and further in a case of the zipper tape 2 made from a polypropylene-based resin, also the thermally fused film 7 and the innermost layer 5 of the bag 1 must be made from the polypropylene-based resin, and this technological limitation still remains unsolved.    i) In the conventional type of zipper for a bag, two sheets of base tapes to be sealed on an inner surface of the bag, and the male strip and the female strip respectively formed on this base tape are integrally formed by an extrusion molding machine.
Because of this requirement, when it is desired to give a specific color to the zipper tape for the purpose to indicate that the zipper tape is attached to inside of an upper open section of the bag or to make the zipper tape colorful, it is necessary to add a coloring material to a resin used as a material for the tape and to extrude the colored resin from the extrusion molding machine.    j) For the reason described above, it is possible to give a specific color to the zipper tape as a whole, but it is impossible to give a color only to the male and female strips, nor to give different colors to the mating section and base tape respectively, and therefore when designing a bag with a zipper, options in designing the zipper section are disadvantageously limited as compared to those allowable in other sections.    k) Further, once the zipper tape has been set in an upper open section of a bag, only a surface of the base tape and the mating section can directly be checked visually, and it is impossible, because of the presence of the mating section, to print on the zipper tape an alerting message such as, for instance, that “If the zipper tape color has not changed to blue, please check and confirm again that the zipper tape has completely be closed” for alerting a user to check whether the mating section has been completely closed. It is desired to print this type of alerting message there.